Hybrid ram air turbine with inlet guide vanes

ABSTRACT

A hybrid ram air turbine includes a generally conical-shaped shaft which mounts a number of vanes wrapped in a substantially helical orientation along the shaft with a portion of each vane being formed in the general shape of a reaction turbine blade and another portion in the general shape of an impulse turbine blade. A number of fixed inlet guide vanes having a convergent wedge shape direct a flow of air onto the blades of the turbine which is mounted within the interior of a pod.

FIELD OF THE INVENTION

This invention relates to submerged ram air turbines, and, more particularly, to a hybrid submerged ram air turbine having a generally conical-shaped shaft that mounts helically wrapped blades formed with a first portion shaped like a reaction turbine blade and a second portion shaped like an impulse turbine blade wherein an air flow is directed onto the blades through a number of fixed, inlet guide vanes.

BACKGROUND OF THE INVENTION

Ram air turbines are commonly used in military and commercial aircraft to provide a source of hydraulic or electrical power in the event of an emergency. Modern aircraft generate power through the main engines or via an auxiliary power unit such as a fuel-burning turbine typically located in the tail of the aircraft In most applications for commercial aircraft, ram air turbines are retracted into the fuselage or wing(s) under normal operating conditions, but are deployed in the event of an emergency loss of power. They typically comprise two or more blades, much like windmill blades, carried by a shaft which is coupled to a generator. The blades rotate the shaft in response to contact with the air stream produced by movement of the aircraft during flight. Depending upon the size of the blades, the capacity of the electrical generator and the flight speed of the aircraft, ram air turbines can supply as much as 70 kW for use in powering flight controls, linked hydraulics and flight-critical instrumentation.

Military aircraft, particularly those designed for electronic warfare, have in the past typically used ram air turbines externally mounted to a pod to deliver power for electronic equipment employed to counter enemy air defenses using reactive and/or pre-emptive jamming techniques, to provide stand-off escort jamming, to initiate electronic attacks and to provide self-protection capability for the aircraft. A pod is essentially a generally cylindrical, aerodynamically-shaped housing mounted to the underside of the aircraft wings. More recently, submerged ram air turbines have been proposed as a replacement for externally mounted designs. The term “submerged” in this context refers to the placement of ram air turbines within the interior of pods in alignment with one or more inlets which direct a flow of air onto the blades of the turbine which is then exhausted through the pod outlet(s).

The increasing sophistication of electronic equipment employed in military aircraft has created a requirement for additional power at flight speeds of 200 to 220 knots. Existing externally mounted and submerged ram air turbines do not provide sufficient power output, and there is a need for an improved turbine design.

SUMMARY OF THE INVENTION

This invention is directed to a submerged, hybrid ram air turbine capable of generating in excess of 60 kW of power when mounted to the pod of an aircraft flying at speeds of about 220 knots

In the presently preferred embodiment, a number of fixed inlet guide vanes are located at the inlet end of the pod having a convergent wedge shape. An air flow is directed by the inlet guide vanes onto the hybrid ram air turbine of this invention which is mounted within the pod interior. The hybrid ram air turbine includes a generally conical-shaped shaft which increases in diameter from the inlet of the pod toward its outlet. A number of vanes are wrapped in a substantially helical orientation along the shaft, and each vane preferably includes a portion formed in the general shape of a reaction turbine blade and another portion formed in the general shape of an impulse turbine blade.

A number of features of this invention contribute to increasing the power output of the turbine herein, which, in turn, results in the generation of more electrical power than prior art designs. The orientation and shape of the inlet guide vanes not only directs flow onto the blades of the turbine, but increases pressure of the air flow at the inlet end of the pod immediately upstream from the turbine blades. The increased, axially extending surface area of the blades, as well as the blade shape, enhances the pressure differential across the blade surfaces to create increased torque. More torque translates into more power. Further, the generally conical shape of the shaft of the turbine reduces the cross sectional area between the shaft and pod wall as the air flow moves from the inlet toward the outlet of the pod, thus tending to maintain more constant pressure along the axial length of the blades which enhances the torque produced.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is side elevational view of the submerged ram air turbine of this invention mounted within the interior of a pod;

FIG. 2 is a front view of the inlet guide vanes for the turbine;

FIG. 3 is a front perspective view of the inlet guide vanes depicted in FIG. 2;

FIG. 4 is a perspective view of the turbine herein; and

FIG. 5 is a schematic view of a turbine blade of this invention, shown apart from the turbine shaft, illustrating the air flow impacting the turbine blades and the forces produced in response to such air flow.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the FIGS., the ram air turbine 10 of this invention is schematically depicted within the interior of a pod 12 of the type which can be mounted to the underside of the wing of an aircraft (not shown). A number of inlet guide vanes 14 are located at the inlet end 16 of the pod 12 in position to direct a flow of air onto the turbine 10, as discussed in detail below. The openings between adjacent guide vanes 14 define passages 18 for the flow of air produced by movement of the aircraft during flight. As best seen in FIG. 3, the guide vanes 14 are preferably formed in a wedge shape that converges toward the turbine 10 so that the cross sectional area of the passages 18 decreases in a direction from the inlet end 16 of the pod 12 toward its outlet end 20. The decrease in cross sectional area of the passages 18 reduces the velocity of the air flow stream and increases its pressure at the inlet end 16 of the pod 12.

The ram air turbine 10 comprises a shaft 22 having a generally conical shape with a planar forward end 24 and planar rearward end 26. The outer surface 27 of the shaft 20 increases in diameter from the forward to rearward ends 24, 26 such that the spacing between the shaft 22 and wall of the pod 12 decreases in a direction from front to rear. See FIG. 1. For purposes of the present discussion, the terms “forward,” “front,” “rearward” and “rear” correspond to the inlet end 16 and outlet end 20 of the pod 12, respectively.

The shaft 22 mounts a number of axially extending blades 28 which are wrapped in a generally helical orientation along the shaft 22 in a forward to rearward direction. A total of five blades 28 are shown in FIG. 4 for purposes of illustration, but it should be understood that a different number of blades 28 may be employed and is considered within the scope of this invention. In the presently preferred embodiment, each of the blades 28 includes a portion 30 having the general shape of a reaction turbine blade and another portion 32 formed in the general shape of an impulse turbine blade.

With reference to FIG. 5, the manner in which torque is created by the configuration of turbine 10 is schematically illustrated. As noted above, the position of the inlet guide vanes 14 and their convergent, wedge-shaped construction is effective to direct a flow of air, represented by arrows 34 in FIG. 5, onto the blades 28. As is well known, reaction turbine blades have a shape generally similar to that of an airfoil and when employed in a reaction turbine a flow of air over the blades induces a lift force created by an increase in pressure along the underside of the blade compared to the pressure on the top of the blade. In FIG. 5, the reaction blade portion 30 of a blade 28 according to this invention is illustrated with a flow of air 34 directed along both the top of the blade 28 and its underside. For purposes of discussion and ease of illustration, the blade 28 shown in FIG. 5 is not wrapped in a helical shape but is elongated, and the “top” of the blade 28 and its “underside” refer to the orientation as shown in FIG. 5. The arrow 36 denotes the lift force created by the air flow 34 along the reaction blade portion 30, which, in turn, applies a torque to rotate shaft 22.

Downstream from the reaction blade portion 30 of the blades 28 is the impulse blade portion 32. Unlike reaction turbine blades, impulse turbine blades create torque by the direct contact of a flow of a fluid at an angle relative to a surface of the blade. As schematically illustrated in FIG. 5, part of the air flow 34 engages the impulse turbine blade portion 32 of the blades 28, creating a force indicated by arrow 38 on the blade 28 which increases the torque applied to the shaft 22. The axial extent of the blades 28, their overall surface area, and, the formation of both reaction and impulse blade portions 30 along the length of blades 28 all contribute to developing increased torque on the shaft 22 compared to existing ram air turbine designs. Increased torque results in increased power output.

The wedge-shaped inlet guide vanes 14, and the generally conical-shaped outer surface 27 of the shaft 22, are intended to assist in maintaining substantially constant pressure from the forward end 24 to the rearward end 26 of the turbine. As noted above, the guide vanes 14 increase pressure at the inlet end 16 of the pod 12 where the forward end 24 of the turbine 10 is located. Although pressure of the air stream 34 is lowered along the top surface of the blades 28 in the reaction blade portion 30 thereof, this effect is counteracted by the narrowing flow path between the outer surface of the shaft 22 and the wall of the pod 12 which tends to increase pressure in the area of the rearward end 26 of the turbine 10. As a result, a more constant pressure is maintained along the pressure side of the blades 28 throughout the length of the turbine 10, Additionally, the outlet end 20 of the pod 12 is preferably provided with one or more exhaust ducts 40, shown schematically in FIG. 1, into which the air flow 34 is directed and expanded after passing the turbine 10. Expansion of the cross sectional area within which the air flow 34 moves creates acceleration of the air flow 34 and helps to “pull” air into the inlet end 16 of the pod 12 at the forward end 24 of the turbine 10 to assist in maintaining pressure on the surfaces of the blades 28.

While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.

For example, while the blades 28 are depicted as having a reaction blade portion 30 closest to the inlet end 16 of pod 12, and an impulse blade portion 32 nearer the outlet end 20, their position could be reversed such that the impulse blade portion 32 is mounted between the inlet end 16 of pod 12 and the reaction blade portion 30 located toward the outlet end 20 of the pod.

Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A turbine, comprising: a shaft having an inlet end, an outlet end and an outer surface, said outer surface of said shaft increasing in diameter from said inlet end toward said outlet end; a number of blades mounted to said shaft, each of said blades extending in a generally helical configuration from said inlet end toward said outlet end, each of said blades being formed with a first portion substantially in the shape of a reaction turbine blade and a second portion substantially in the shape of an impulse turbine blade.
 2. The turbine of claim 1 in which said first portion of each of said blades is located between said inlet end of said shaft and said second portion.
 3. The turbine of claim 1 in which said second portion of each of said blades is located between said inlet end of said shaft and said first portion.
 4. The turbine of claim 1 further including a number of inlet guide vanes located in a position to direct a flow of air onto said blades, each of said inlet guide vanes having a wedge shape that converges toward said inlet end of said shaft.
 5. An apparatus, comprising: a housing having a hollow interior formed with an inlet end and an outlet end; a turbine including: (i) shaft located with said hollow interior of said housing, said shaft having an outer surface increasing in diameter from said inlet end toward said outlet end of said housing; and (ii) a number of blades mounted to said shaft, each of said blades extending in a generally helical configuration from said inlet end toward said outlet end, each of said blades being formed with a first portion substantially in the shape of a reaction turbine blade and a second portion substantially in the shape of an impulse turbine blade; a number of inlet guide vanes located at said inlet end of said housing in position to direct a flow of air onto said blades, each of said inlet guide vanes having a wedge shape that converges toward said inlet end of said housing.
 6. The apparatus of claim 5 in which said first portion of each of said blades of said turbine is located between said inlet end of said housing and said second portion.
 7. The apparatus of claim 5 in which said second portion of each of said blades of said turbine is located between said inlet end of said housing and said first portion. 